Grain hydrogen trap

Hydrogen trapping This is the binding of hydrogen atoms to impurities and structural defects. Hydrogen may be trapped at mobile dislocations or grain boundaries. 

On a more positive note, it seems clear that steels can be made more resistant to the effects of hydrogen by incorporating as many strong, finely dispersed traps in the microstructure as is possible, while ensuring that there are no continuous trap sites (such as embrittled grain boundaries). 

The atmosphere is also important in sintering. Gas trapped in closed pores will limit pore shrinkage unless the gas is soluble in the grain boundary and can diffuse from the pore. Alumina doped with MgO can be sintered to essentially zero porosity in hydrogen or oxygen atmospheres, which are soluble, but not in air, which contains insoluble nitrogen. The density of oxides sintered in air is commonly less than 98% and often only 92-96%. The sintering atmosphere is also important in that it may influence the sublimation or the stoichiometry of the principal particles or dopants. 

In the above approximation the total number of traps in 1cm3 of the probe, calculated from hydrogen amount, is Z=2Zi=2.34T06 cm3, and the grain concentration is 2.58 106cm 3. The concentrations coincide within 10%. 

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